Bosch D296 Application Manual page 2

D296/D297 | Application Guide | 1.0
Trademarks
The National Fire Alarm Code
trademark of the National Fire Alarm Association, Inc.
Notice
Before installing any fire alarm system,
consult your local authority having
jurisdiction (AHJ).
1.0 Introduction
Use this document to determine the best
locations and applications of the
D296/D297 Series Projected Beam
Smoke Detectors.
Use the D296/D297 Series:
•
Where there are high ceilings such as in atriums
and aircraft hangers. Mount the detectors on walls
for easy access.
•
In dusty environments such as warehouses,
factories, and barns. These detectors have built-in
compensation to prevent alarms caused by dust.
•
Where there are expansive ceilings. One set of
D296/D297 Series can replace up to 24 spot type
smoke detectors. This saves on service and
installation costs, especially in areas such as large
offices or department stores.
•
On ornamental ceilings where spot detectors are a
distraction.
•
Where there is limited access to the ceiling such as
in factories and warehouses.
The detectors have separate transmitters and receivers.
The transmitter projects an infrared (IR) beam across
the protected area to a receiver containing a
photosensitive cell that monitors the signal strength of
the light beam.
The D296/D297 Series Projected Beam Smoke
Detectors work on the principle of obscuring light. Its
photosensitive element sees light produced by the
receiver in a normal condition. The receiver is
calibrated to a preset sensitivity level based on a
percentage of total obscuration. Beam length and the
desired response time determine this sensitivity level.
The installer can choose from eight sensitivity settings
based on the length of the beam used in a particular
application.
2
Introduction
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is a registered
The transmitter can be independently powered from
the receiver, greatly reducing wiring runs and
installation cost. Since battery backup is required for
fire alarm systems, battery backup is required for the
transmitter whether it is powered from the control
panel or is independently powered.
Unlike spot type photoelectronic smoke detectors,
beam smoke detectors are generally less sensitive to the
color of smoke. A beam smoke detector might be
suited to applications inappropriate for spot-type
photoelectronic detectors, such as applications where
the anticipated fire would produce black smoke. Beam
smoke detectors require visible smoke and might not
be as sensitive as ion detectors in some applications.
Beam smoke detectors are sensitive to the cumulative
obscuration presented by a smoke field. A combination
of smoke density and the linear distance of the smoke
field create this obscuration across the projected light
beam. Cumulative obscuration is a measure of the
percentage of light blockage.
Since the sudden and total obscuration of the light
beam is not a typical smoke signature, the detector sees
this as a trouble condition, not an alarm. This threshold
is at a sensitivity level that exceeds 90% to 95% total
obscuration. This minimizes the possibility of an
unwanted alarm due to the blockage of the beam by a
solid object such as a sign or ladder inadvertently
placed in the beam path.
Very small, slow changes in the quality of the light
source are not typical of a smoke signature. These
changes can occur because of environmental conditions
such as dust and dirt accumulation on the transmitter,
the receiver's optical assemblies, or both. Generally,
the automatic environmental compensation circuit
compensates for these changes. When you initially turn
on the detector and run the setup program, it assumes
the light signal level at that time as a reference point
for a normal condition. Over time, the quality of the
light signal degrades (perhaps due to dust), and the
environmental compensation circuit compensates for
this change. The compensation rate is limited, ensuring
the detector remains sensitive to slow or smoldering
fires. When the automatic environmental compensation
circuit no longer compensates for signal loss (as with an
excessive accumulation of dirt), the detector signals a
trouble condition.
The receiver indicates a trouble condition if the beam
strength increases more than 20%. An incorrectly
aligned transmitter and receiver or a partially blocked
beam can cause a trouble when the transmitter and
receiver are installed.
Bosch Security Systems, Inc. | 01/07 | F01U500951-01